Abstract
粒線體去氧核醣核酸的演化速率遠大於細胞核去氧核醣核酸，所以粒線體 核酸序列相似度之高低常被生物學家當作探討動物血緣遠近的指標。在粒 線體核酸序列中又以替位環部分的演化速率最快，而核醣體核醣核酸基因 則演化速率較慢。前人的報告指出在脊椎動物的粒線體去氧核醣核酸中， 核醣體核醣核酸基因是位在替位環的附近。然而，最近有報告認為北京鴨 粒線體的核醣體核醣核酸基因位在替位環下游約9 kb處。實驗中，我們定 出番鴨及菜鴨粒線體去氧核醣核酸中替位環部分其核醣體核醣核酸基因之 核酸序列。將此核酸序列與雞的粒線體核酸序列作比較，證明番鴨及菜鴨 其粒線體的核醣體核醣核酸基因與替位環緊密相連。且其粒線體去氧核醣 核酸存在一種特殊的基因排列方式。而前人的研究發現這種基因排列方式 也普遍存在雞、雉雞等鳥類的粒線體去氧核醣核酸中。經類緣關係樹形圖 分析，得知，這兩屬鴨子與雞比其他動物有更近之類緣關係。由聚合□鏈 鎖反應的結果，顯示同種的鴨類，雖然其外型有極大之不同，然而其粒線 體去氧核醣核酸的序列可能完全相同或極為相似。 Mitochondrial DNA (mtDNA) is an extremely usefu l molecule in assessing relationships among species and populations that diverged rather recently sin ceit has a higher evolutionary rate than that of nu clear DNA. Sequence analysis of vertebrate mtDNAs h as revealed that the displacement loop (D-loop) re gion is the most rapidly evolving part of genome, w hile the ribosomal RNA genes are quite conservative . These DNA fragments are known to adjacent to eac h other inall the vertebrate mtDNA examined. Howeve r, it has recently been reported thatthe ribosomal RNA genes from Pekin duck is located 9.5 kb down s tream of D-loop.In order to understandthe discrepa ncy in the gene locations, we cloned and sequenced the mtDNA fragments containing D-loop region and ad jacent segment from two different genera of ducks (Cairina and Anas). By nucleotide sequence determin ations and homologous comparisons with chicken mtDNA quence, we demonstrated that the D-loop and ribosomal RNA genes are adjacent to each other in mitochondria chondria of these two avians. A novel gene order(N D6-tRNAGlu-D- loop) which conserved among the galli form birds also exists in these two avians. Phylogen etic analysis of these two genera of ducks, showed that the duck and chicken are come from a common a ncestor. From the result of avians mtDNA polymearase chain reaction (PCR) amplication, indicated that the avians which are taxis to the same species, alt hough their morphology are very different, may have the same or very similar mtDNA sequence. Thus, mt DNA is apowerful tool in phylogenesis analysis of related animals.